Intraluminal, intracavity, intravascular, and intracardiac treatments and diagnosis of medical conditions utilizing minimally invasive procedures are effective tools in many areas of medical practice. These procedures are typically performed using imaging and treatment catheters that are inserted percutaneously into the body and into an accessible vessel of the vascular system at a site remote from the vessel or organ to be diagnosed and/or treated, such as the femoral artery. The catheter is then advanced through the vessels of the vascular system to the region of the body to be treated. The catheter may be equipped with an imaging device, typically an ultrasound imaging device, which is used to locate and diagnose a diseased portion of the body, such as a stenosed region of an artery. For example, U.S. Pat. No. 5,368,035, issued to Hamm et al., the disclosure of which is incorporated herein by reference, describes a catheter having an intravascular ultrasound imaging transducer. These are generally known in the art as Intravascular Ultrasound (“IVUS”) devices.
FIG. 1 shows an example of an imaging transducer assembly 1 known in the art. The imaging transducer 1 is typically within the lumen 10 of a guidewire or catheter (partially shown), having an outer tubular wall member 5. To obtain an image of a blood vessel the imaging transducer assembly 1 may be inserted into the vessel. The transducer assembly 1 may then interrogate the cross-sectional-plain of the vessel from the inside by rotating while simultaneously emitting energy pulses, e.g., ultrasound pulses, and receiving echo signals.
On the distal end of the assembly 1 is an imaging element 15, specifically, an imaging transducer 15 that includes a layer of piezoelectric ceramic (“PZT”) 80, “sandwiched” between a conductive acoustic lens 70 and a conductive backing material 90, formed from an acoustically absorbent material (e.g., an epoxy substrate having tungsten particles). During operation, the PZT layer 80 is electrically excited by both the backing material 90 and the acoustic lens 70 to cause the emission of energy pulses.
The transducer assembly 1 of FIG. 1 shows a single imaging element 15. Also known in the art is the utilization of an array of imaging elements, e.g., an array of imaging transducers, instead of just one imaging element 15. An array of imaging transducers provides the ability to focus and steer the energy pulses without moving the assembly 1. An example of such an array 100 is shown in FIG. 2, which also illustrates a known process 200 for creating the array 100, commonly referred to as “dice and fill.” In the process 200, a plate of poled PZT ceramic 210 is obtained. A saw 220 is then used on the ceramic 210, forming a plurality of kerfs 230 and an array of posts 240, which serve as the PZT layer for the array of transducers 100. The kerfs 230 are then backfilled with polymer materials, such as epoxy 250, to form composite structures. Transducers based on this architecture can exhibit high bandwidth, high sensitivity, good acoustic impedance matching to tissue, and desirable array properties such as low inter-element cross-talk and low side-lobe levels. However, transducers based on this architecture generally do not operate at frequencies much above 20 Megahertz (“MHz”). Accordingly, an improved imaging device would be desirable.